The present invention relates to a Schottky barrier diode (hereinafter abbreviated as an SBD), which is a semiconductor rectifying device utilizing a Schottky barrier formed on an interface of a metal and a semiconductor.
An SBD utilizing a Schottky barrier formed on an interface of a metal and a semiconductor has a trade-off relationship between forward characteristics and backward characteristics. It is therefore necessary to adjust the height (hereinafter referred to as xcfx86b) of the Schottky barrier [refer to P.378, S. M. Sze. xe2x80x9cPhysics of Semiconductor Devicesxe2x80x9d].
If a silicon wafer is used as a semiconductor substrate, xcfx86b is controlled in the following two methods:
(1) A barrier metal is selected [in this case, an interface is an metal/silicon interface. Refer to, e.g., the above-mentioned xe2x80x9cPhysics of Semiconductor Devicesxe2x80x9d]; and
(2) A silicide layer is controlled [in this case, the interface is a metal silicide/silicon interface. For example, refer to Odomari, Hara, Chikyo, Applied Physics, vol.56, (1987), pp.311-331, xe2x80x9cStructure of Silicide/Silicon viewed with Electronic Standardsxe2x80x9d]
In the first method (1), xcfx86b ordinarily depends on a difference between a work function of the metal and an electron affinity of the semiconductor. The work function and the electron affinity are values that are specific to the materials. Therefore, xcfx86b can be controlled to some extent by selecting a metal material, but it cannot be finely adjusted.
In the second method (2), a heat treatment forms the Schottky barrier on the metal silicide/silicon interface, not on the metal/silicon interface. The composition of the metal silicide depends on a heat treatment temperature, and thus, xcfx86b can be changed according to the heat treatment temperature. The second method (2), however, is not universal since it is not easy to perform and there is a limitation on the materials.
In the above methods, a desired xcfx86b cannot be acquired since it is determined by the work function specific to a single metal or the metal silicide.
It is therefore an object of the present invention to provide an SBD, which is able to adjust the forward characteristics and the backward characteristics by precisely controlling the barrier height xcfx86b.
The above object can be accomplished by providing an SBD comprising a barrier metal formed of an alloy, which is composed of two or more kinds of metal materials in combinations that provide different xcfx86b with respect to a semiconductor and that form no intermetallic compound.
If an alloy composed of two kinds of metals A and B is an eutectic alloy, the alloy has such a structure that the metal A and the metal B are mixed very finely. Thus, the SBD having the barrier metal formed of such an alloy has an intermediate xcfx86b between barrier heights of the SBDs, which are formed of single metals. For this reason, adjusting the composition of the alloy enables the SBD to have xcfx86b that cannot be achieved by a single metal, and makes it possible to precisely control electric characteristics.
A combination of two kinds of metals in an alloy constituting said barrier metal is a combination of scandium and erbium, yttrium (hereinafter referred to as Y), titanium (hereinafter referred to as Ti), manganese (hereinafter referred to as Mn), zirconium (hereinafter referred to as Zr), vanadium (hereinafter referred to as V), ciromium hereinafter referred to as Cr), tantalum (hereinafter referred to as Ta), molybdenunm (hereinafter referred to as Mo) or platinwn (hereinater referred to as Pt); a combination of erbium and Y, Ti, 7r, V, Ta or Mo; a combination of Ti and Zr, VY Cr, nickel (hereinafter referred to as Ni), Ta or Mo; a combination of M and V, cobalt or Ta; a combination of Zr and Ta; a combination of V and Cr, Ta or Mo; a combinton of Cr and Ni or Mo; a combination of Ni and Pt; or a combination of Ta and Mo.
If the alloy is composed of two or more metal materials in a combination that forms an intermetallic compound, the alloy has such a structure that one metal A or B and the intermetallic compound are finely mixed. The SBD having the barrier metal that is composed of such an alloy is considered to have an intermediate xcfx86b between the metal A and the intermetallic compound. xcfx86b of the intermetallic compound, however, does not necessarily take an intermediate value between the metal A and the metal B. Therefore, xcfx86b of the alloy cannot be found from xcfx86b of a single metal, and xcfx86b of the alloy cannot be controlled. Likewise, xcfx86b cannot be controlled in the case where there are many intermetallic compounds, because the intermetallic compounds may be finely mixed in the alloy.